The sea contains numerous different types of seafloor mineral deposits such as mineral sands, diamonds, rock phosphates, seafloor massive sulphides, nodules, and hydrates. Many of these deposits are located in deep water but at a relatively shallow depth below the seafloor. Accordingly, seafloor drill assemblies are being developed for sampling techniques (as opposed to vessel operated drilling rigs). Furthermore, seafloor drilling is also now being used for geotechnical evaluation. It is therefore important to achieve good quality and high recovery of core samples from below the seafloor.
Seafloor based drilling assemblies have many challenges that are required to be overcome. One of these challenges is how drilling fluid is provided to a seafloor drilling assembly while ensuring quality of the fluid is maintained. The benefits of using drilling fluids to assist while drilling holes to obtain core samples are well documented. Drilling fluids, also referred to as “drilling mud”, are introduced through the drill string to facilitate the drilling process by removing cuttings, stabilizing the hole, improving penetration rates, enhancing core recovery and cooling and lubricating the coring bit and drill string. The delivery of drilling fluid is largely routine in surface based drilling, shallow water drilling or rig based drilling. However, the delivery of drilling fluid becomes more problematic in seafloor based drilling assemblies.
To date the only method of providing drilling fluid to the seafloor operated drilling assembly is to use a drilling fluid concentrate. This drilling fluid concentrate is mixed with sea water at the sea floor during the drilling operation using an inline mixer. Unfortunately, the subsequent mixed drilling fluid is often of inconsistent quality and the concentration and quantity required is often inadequate. Further, the measure of the quality of the drilling fluid is difficult to assess before use.
The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge in Australia.